1. Field of the Invention
The invention relates to a fuel cut-off valve. More particularly, the invention relates to a fuel cut-off valve that prevents fuel vapor inside a fuel tank of a vehicle or the like from flowing out to a canister and adhering to an adsorbent provided in the canister. The fuel cut-off valve according to the invention also prevents fuel in the fuel tank from flowing out to the canister when the fuel level rises.
2. Description of the Related Art
A fuel tank that stores fuel supplied to a combustion chamber of an engine is provided in a vehicle or the like. This fuel tank has a ventilation system that lets air in and out corresponding to decreases and increases in the amount of fuel in the tank. This ventilation system is formed as a system that provides communication between the inside of the fuel tank and a canister. If the fuel tank overflows, the spilled fuel flows out to the canister side, saturating the canister and thus rendering it useless. Therefore, a tank-full control valve is provided at an upper portion of the fuel tank. When the tank is full of fuel, the ventilation system closes off so that air and fuel will not flow out to the canister side.
In addition to the tank-full control valve, the fuel tank is also provided with a fuel-spill prevention valve that controls pressure fluctuation in the fuel tank by normally being open to the outside air, and which closes when the vehicle is inclined or rolls or the like. The tank-full control valve and the fuel-spill prevention valve may be provided separately. However, in order to keep costs down, a fuel cut-off valve having the functions of both of these valves is described in Japanese Patent Application Publication No. 2004-257264 (JP-A-2004-257264).
This fuel cut-off valve is shown in FIGS. 24 and 25. This fuel cut-off valve 1 houses an upper float 4 and a lower float 5 in an internal space 3 formed by a case 2. An upper opening 8a is provided above the internal space 3, a lower opening 8b is provided below the internal space 3, and a side hole 14 is provided in the upper peripheral wall surface of the case 2. Most of the case 2 is inserted into a fuel tank 6. A flange 7 formed horizontally on the upper outer peripheral wall of the case 2 is mounted to the upper wall surface of the fuel tank 6.
The lower float 5 is a member that rises when fuel in the fuel tank 6 enters the internal space 3 through the lower opening 8b. A first valve member 9 that is rod-shaped and has a small diameter is formed on the upper surface of the lower float 5. A second valve member 4a that is ring-shaped and has a large diameter is provided on the upper surface of the upper float 4. The upper float 4 is attached so as to be able to move up and down above the lower float 5. Also, the upper float 4 has a small diameter upper end opening 12 in the center. A first valve seat 10 against which the small diameter first valve member 9 of the lower float 5 may abut is formed on the lower end portion of this small diameter upper end opening 12.
A second valve seat 11 is formed on the lower end portion of the large diameter upper opening 8a, so that if fuel enters the internal space 3 through the lower opening 8b when the fuel tank 6 is being filled, for example, the lower float 5 and the upper float 4 will rise together and the small diameter first valve member 9 of the lower float 4 will abut against the first valve seat 10 of the upper float 4, thereby closing off the small diameter opening 12, while the second valve member 4a of the upper float 4 will abut against the second valve seat 11 formed on the lower end portion of the upper opening 8a, thereby closing off the large diameter upper opening 8a. As a result, fuel is prevented from flowing out to a canister, not shown, via a communication passage 13 above the upper opening 8a. 
When the first valve member 9 and the second valve member 4a are closed, for example, the force with which the small diameter first valve member 9 abuts against the first valve seat 10 from the pressure inside the fuel tank 6 is much less than the force with which the large diameter second valve member 4a abuts against the second valve seat 11. Therefore, if the pressure inside the fuel tank 6 drops even slightly, the lower float 5 will fall under its own weight, such that the small diameter first valve member 9 will no longer abut against the first valve seat 10. As a result, the inside of the tank 6 will be communicated with the outside air via the small diameter upper end opening 12 and the side hole 14.
As a result, the pressure inside the fuel tank 6 will drop, such that the large diameter second valve member 4a will immediately come away from the second valve seat 11, thereby opening the large diameter upper opening 8a to the outside air, which will cause the pressure inside the fuel tank 6 to fall rapidly. Also, even if the lower opening 8b is closed off by fuel, for example, when the fuel tank 6 is full, the side hole 14 is provided in the side wall surface of the case 2, so fuel vapor produced inside the fuel tank 6 will flow through the side hole 14 toward the communication passage 13, thus preventing the pressure in the fuel tank 6 from becoming excessively high.
In this way, the fuel cut-off valve 1 according to the related art functions as both a tank-full control valve and a fuel-spill prevention valve, and is thus advantageous in terms of both cost and convenience.
The upper float 4 of the fuel cut-off valve 1 is provided with four mounting members 4b, each having an engaging groove 4c as shown in FIG. 25 on the lower surface, at equidistant locations concyclically. Also, the lower float 5 has a large diameter portion 5a and a small diameter portion 5b, and four retaining members 5c are provided at equidistant locations concyclically on the upper outer periphery of the small diameter portion 5b. 
The engagement of these members will now be described. That is, the members engage by the upper float 4 being pushed down onto the upper portion of the lower float 5. At this time, the retaining members 5c of the lower float 5 fit inside the mounting members 4b of the upper float 4 while pushing the mounting members 4b to the outside. When the retaining members 5c reach the engaging grooves 4c in the mounting members 4b, the retaining members 5c fit into those engaging grooves 4c and the mounting members 4b spring back (i.e., return) to their original state. As a result, the lower float 5 and the upper float 4 are connected in a state in which they can move up and down a predetermined distance together.
When the valve is abutting against the valve seat, less offset results in a better seal between the valve and the valve seat. With the fuel cut-off valve 1, there is a slight gap between the outer periphery of the lower float 5 of the fuel cut-off valve 1 and the inner periphery of the case 2, so the lower float 5 is able to move laterally by an amount corresponding to the size of that gap. Also, the upper float 4 is smaller than the lower float 5 and is provided so as to be able to move a predetermined distance up and down with respect to the lower float 5. Further, there is also a slight gap between the mounting members 4b and the retaining members 5c in the lateral direction, so the upper float 4 is also able to move laterally by an amount corresponding to the size of that gap.
The lower float 5 is able to move laterally by an amount corresponding to the size of the gap between the outer periphery of the lower float 5 and the case 2, and the upper float 4 is able to move laterally farther than the lower float 5, or more specifically, by the cumulative distance of the gap between the outer periphery of the lower float 5 and the inner periphery of the case 2, and the gap between the upper float 4 and the lower float 5.
As described above, the upper float 4 of the fuel cut-off valve 1 is able to move laterally by the total distance of the gap between the outer periphery of the lower float 5 and the inner periphery of the case 2, and the gap between the upper float 4 and the lower float 5. Therefore, for example, even if there is a lateral offset of that amount, the large diameter second valve member 4a can still abut against the large diameter second valve seat 11, so no particular problems arise.
However, if a seal is achieved between the second valve member 4a and the second valve seat 11 while the lateral offset of the upper float 4 is greater than the gap between the outer periphery of the lower float 5 and the inner periphery of the case 2, for example, it becomes necessary to align the upper float 4 in order to seal between the small diameter first valve member 10 and the first valve seat 9. However, because the second valve member 4a is abutting against the second valve seat 11 in this case, a large amount of force is required to align the upper float 4, and as a result, the upper end opening 12 may not be sufficiently closed off.
With a conventional fuel cut-off valve, the gap is made as small as possible to reduce any offset. This is also true for the gap between the mounting members 4b and the retaining members 5c. However, as described above, the lower float 5 is placed into engagement with the upper float 4 while pushing and spreading the mounting members 4b of the upper float 4 outward. Therefore, the mounting members 4b must be made to be able to deform to some degree, and thus are susceptible to secondary deformation during engagement or as a result of a change in the environment, for example. Deformation of the mounting members 4b may result in greater offset.